Electronic gating circuits



H. KARP ETAL ELECTRONIC GATING CIRCUITS Filed Feb. 15, 1949 oct. 14, 1952 /N VEN TORS HARVEY KARP ROBERT DARDEMJR. MICHAEL E KOLUDZIEJ ATTORNEY at the end of the trace.

Patented Oct. 14, 1952 ELECTRONIC GATING vCIRCUITS Harvey Karp, Waltham, Mass.,.obert R. Darden,

J r., 'Solroman ,(lalif., and Michael F. Kolcdziej, Waltham, tpMass., assignors to VRaytheon lillanu.- facturing,CompailnNewtom Mass a corporan.

tion of Delaware Application February 15, 1949, xSeriol .No-y ifig y Claims. (CifZ50-L27)` This application relates to electrondischarge circuits and more particularly to a gating `circuit whereby received signals maybe passed or..re `jectcd periodically.

In radar systems of the pulse-echo type, it is necessary that the electron beam in the cathode ray tube be turned 01T dur-ing the retrace period, so that signals received during the retrace period will not appear onrthescope to be .confused with signals received during the normaltraceperiod. Furthermore, in some Ycases it-is desirable that the electron beam and the signal amplifier, when turned on, be brought up to precisely the threshold Where signals will be passed. and .presented on the screen. This is desirable in order that .all the signals received be presented on the scope. If the threshold level is exceeded by the gating pulse, this pulse will be fed through to .the cathode ray screen, thus reducing thesignalrto background contrast which would normally appear on the screen. n

Therefore, it is an object of this invention to provide@J gating circuit which willr accuratelyigate thesignals applied to the cathode ray tube.

It is a further object of this invention to providega gatingv circuit wherein interference from the gating operation does not appearyonythe screen.

Another object of this invention isitoprovide'a gating circuit wherein the .widthof 17116 :gate-is maintained constantv regardless of the strength of the received signalsA thereby eliminating jitterl Other and furtherobjects of `thisinvention will berapparent as the description thereof progresses, reference -being had totheaccompanying drawing wherein: i

The single Viigure represents a schema-tic diagram of an embodiment of the invention.`

Referring now to the drawing there is `shown a pulse generator I which generates pipsl of, `for example, a few microseconds duration Yin o re` sponse to a sine waveinp-ut from a master oscillator with the pips occurring once every cycle of the input sine wave.` `This may be -accomplished by any of severalwell-known pip .generators.

The pips, which arenegative are `fed through a condenser 2 `to the grid 3 ofoa tube 4 which is one section of a two-tubemultivibrartour.l The grid 3 .is connected Ato B+ .through a grid resistor `5. The plate 6 of tube 4 is connectedto Bjthrough a plate loadlresistor 1. The cathodeothetube 4 is connected to :the 4 ca thodedl `of theitube lll which the second section of thE :two-,tubg multi-,-

2 vibrator. The `two cathodes 8 and 'i9 are ,connected to a source of negative potential through a resistor Il. The grid l2 of the tubelil is connected to the midpoint of the voltage dividernetwork comprising a resistor I3 which is: connected to B-land resistor I4iwhich is connected toa source of negative potential. In the particular circuit shown B+ is 275 volts 4and thelnegative potential is Volts; However, these values-may be varied considerably.` The plate l5 of tube i Unis connected through a resistor It toB-land also through a condenser. 49 to the grid 3 of tube 4. The values of the resistors I3 and 4Ht are such that in the absence of :a pip from the pulsegenerator thegrid-IZ is normally below cutoii, The

grid 3 which is normallyabove cut-oihdue to its connection toB-ithrough resistor 5,.thus caus-4 ing the tube 4 to 4conduct heavily, is driven negar' tive by a pip from `the pulse generator lil. This causes a decrease in current through the cathode resistor Il which is common tobothftubes!! and It. This lowers thepotential cof cathode 9 until thev tube .l0 .isvno .longer cutoff. `.Current iiovvsl through .tubelll and the plateresistor 46 cans--l ing the plate l5 .oftube f1,0 to befdriven negative. This negativeY potential is'coupled through the condenser .49 to ,the grid 3 of .tube 4 causing Athe tube .4 to go into Icutoi. r Thentube 4 :remains out off until the. oondoosorl 49.- ohorsoo sofficieritly` through ythe A resistor 5 andA the n parallel -combina tion of resistor lxand resistormll; to allow jthe tubev 4 vto conduct, whereupon current through,

the Cathode resistor begins ,inoroaoinc themas of tube `i0 ,thereby decreasing'othe 1currentilow ,in

l0 is t thus driven positivo driving. .thasrid :.3 of

the cathodes and e9 of themultivibrator.V vPlate I9 of the Ytube |.8 is connected .through a Lresistor 2t ,to B+.V Thofrosistor 2.0;; may Vbe: -eliroinated;

howevenit is `shown hereasa inea-nsofyproduc-Y ins positive oulsoowhiohgmarbo used to trigger other circuits in the; equipment. The: ,cathode 2l` of tubel8 is connected---toanothercathodei of a tube 23; land yto ,ground through :a cathode load resistor`24. 1 The plate 125. ,of `tube 2 3; is .connected through la -resistort` to B+. The grd 21. of the tube 23 is connected to the variable tap of ia This negative pulse is fed through a resistor 29 to the cathode 30 of gating tube 3|. yThe grid 32 is connected to ground through a grid resistor 33 which is bypassed by a germanium rectier 34 connected thereacross which functions as a D. C. restorer. The grid 32 is fedfrom a receiver and video amplifier 35 of the radar system. The Aplate 35 of the gating tube 3| is connected to B+ through a resistor 31, an inductance 33 and decoupling resistor 39. The plate 36 of the gating-E tube is connected to an amplifier 42 which feeds" the grid 430i the cathode ray tube 44. The cathode ray tube 44 as shown here is a P. P. I. tube in a radar set having the standard sweep circuits and wherein targets are presented on the screen by intensity modulation vthrough the grid 43. By adjusting the tap of potentiometer 28, the current through tube 23 may be varied, thus varying the quiescent potential across cathode load resistor 24.This potential across resistor 24 is adjusted so that when a negative pulse is applied to the grid of tube I3 the gating tube 3| will be precisely at its cutoff point, and in the absence of a pulse on grid l1 the gating tube 3| will be well below cutoff.

Therefore', 'when a pulse is applied to grid Il and the tube 3| is exactly at cutoff, positive signals fed to the grid 3| will be passed `by the tube 3| amplified bythe `amplifier 42 and presented as positive pulses. The inductance 38, vwhich is a high impedance to high frequencies, causes the gain of the tube 3| to be larger at yhigh frequencies, thus increasing the band width and frequency response of the gate 3|. Also, the resistor'29 causes considerabledegeneration to the amplification of tube 3|,' thereby improving the linearity of amplification of tube 3|.

'It may be noted that small positive signal pulses appearing on the grid 32 of the gating tube 3| Will be amplified very littlesince they will cause operation of the gating tube on the nonlinear, low gain portion of the tubes characteristic curve. However, these small signals will be operating on a rhigh gain portionv of the char--v acteristic curves of both the video amplifier 35 preceding the gating tube 3| and the amplifier'.

42 fed by tube 3|, while excessively large signals will be limited by the video amplifier 35 and am- Therefore, the overall eiect will be an emphasis of low amplitude signals for presentation on the screen of tube 44.

It may be noted that, by reason of the manner in which the gating pulse is applied to gating tube 3|, no signals from the gating pulse operation appear on the screen, whereas, if the gating pulse were applied by some other means as, for example, a condenser or transformer, objectionable pips at thebeginning and ending of each gating pulse would'be fed through to the grid 43 of the cathode ray tube'. Furthermore, since the tube I8 is a cathode follower, it eiectively isolates the multivibrator tubes 4 and IB from loadingv by the gating circuit whereby the variations in the load due to received signals cannot feed back to the multivibrator to change its gating time. This'eliminates jitter at the end of the trace. f y

The germanium rectifier 34 shown here eliminates undesirable negative bias shifting which may be applied to the grid 32 of the gating tube, thus retaining the grid in a position to properly respond to all positive pulses received from the' receiver and l'video amplifier 35.

Atube-45 having its plate 46 and cathode 4l in parallel with the plate 36 and cathode 30, respectively, of tube 3|, and its grid 41, connected to a source of pulses, may be used to inject additional signal information in the form of range markers and video signals.

'I his completes the description of the illustrated embodiments of this invention. However, many modifications will be apparent topersons skilled in the art. For example, the standard A scope presentation could be used instead of the P. P. I. presentation and many different types of gate generators Well known in the art could be substituted for that shown; Accordingly, applicant does not wish to be limited to the specic details of the invention described herein except as defined in the appended claims.l

What is claimed is:

1. An electrical circuit comprising av signal input channel, a gating tube fed by said channel, a source of rectangular pulses, means fed Yby said source and connectedto said gating tube for applying said pulses to Asaid gating tube to periodically render'said tube nonconductive to signals from said channel and for preventing changes in conduction of said gating tubev from affecting said 'pulse source, and a phase-inverting amplier connected to said gating tube whereby small signals which are amplified a small amount relative to large signals by said gating tube will be amplified a large 'amount relative to large signals by said amplifier.

2. An electrical circuit comprising a gating tube having a source of electrons, a control electrode, an anode, a signal input channel connected to said control electrode, a source of rectangular pulses, means fed by said source and connected to said gating tube for applying said pulses to said gating tube to periodically render said tube nonconductive to signals from said channel, means connected to said'gating tube for adjusting the bias of said gating tube, and a phaseinverting amplier connected to rsaid gatingtube whereby small signals which are amplified a small amount relative to large signals by said gating tube will be amplified a large amount relative to large signals by said amplifier. y

3. An electrical circuit comprising a signal input'channel, a gating tube fed by said channel, a source of rectangular pulses, means-fed by said source and connected to said gating tube for applying said pulses to said gating tube to periodically render said `tube nonconductive to signals from said channel, means connected to said gating tube for adjusting the bias of said gating tube comprising a second tube having a cathode circuit comprising an impedance in the cathode circuit of said gating tube, and means connected to said second tube for adjusting the current flow through said-second tube. v

4. Anr electrical circuit comprising a signal input channel, agating tube fed by said channel, a source of rectangular pulses, and means fed by said source and connected to `said gating tube for applying said pulses to said gating tube to periodically render said tube nonconductive to signals from said channel comprising avcathode follower whose cathode is'connected to the cathode of said gating-tube through an impedance.

5. An electrical circuit comprising a signal input channel, a gating tube fed by said channel, a source of rectangular pulses, and means fed by said source and connected to said gating tube for applying said pulses to said gating tube to periodically render `said tube nonconductive to signals from said channel comprising a cathode follower connected to lthe cathode circuit of said gating tube through a resistance.

6. An electrical circuit comprising a signal input channel, a gating tube fed by said channel, a source of rectangular pulses, means fed by said source and connected to said gating tube for applying said pulses to said gating tube to periodically render said tube nonconductive to signals `from said channel and forl preventing changes in conduction of said gating tube from affecting said pulse source comprising a cathode follower, and a phase-inverting amplifier connected to said gating tube whereby small signals which are amplified a small amount relative to large signals by said gating tube will be amplied a large amount relative to large signals by said amplier.

7. An electrical circuit comprising a signal input channel, a gating tube fed by said channel, a source of rectangular pulses, means fed by said source and connected to said gating tube for applying said pulses to said gating tube to periodically render said tube`nonconductive to signals from said channel and for preventing changes in conduction of said gating tube from aiecting said pulse source comprising a cathode follower connected to the cathode circuit of said gating tube, and a phase-inverting amplifier connected to said gating tube whereby small signals which are amplified a small amount relative to large signals by said gating tube will be amplied a large amount relative to large signals by said amplifier.

8. An electrical circuit comprising a signal input'channel, a gating tube fed by said channel, a source of rectangular pulses, means fed by said source and connected to said gating tube for applying said pulses to said'lgating tube to periodically render said tube nonconductive to signals from said channel and for preventing changes in conduction of said gating tube from affecting said pulse` source, means connected to said gating tube for adjusting the bias of said gating tube, and a phase-inverting amplifier connected to said gating tube whereby small signals which are amplified a small amount relative to large signals by said gating tube will be amplified a large amount relative to large signals by said amplifier.

9. An electrical circuit comprising a signal input channel. a gating tube fed by said channel, a source of rectangular pulses, means fed by said source and connected to said gating tube for applying said pulses to said gating tube to periodically render said tube nonconductive to signals from said channel and for` preventing changes in conjunction of said gating tube from affecting said pulse source comprising a cathode follower. and means connected to said tube for adjusting the mean bias of said gating tube comprising a second tube having a cathode circuit vcomprising an impedance in the cathode circuit of said gating tube.

10. An electrical circuit comprising a signal input channel, a gating tube fed by said channel, a source of rectangular pulses, means fed by said source and connected to said gating tube for applying said pulses to said gating tube to periodically render said tube nonconductive to signals from said channel and for preventing changes `in conduction of said gating tube from affecting said pulse source comprising a cathode follower connected to the cathode circuit of said gating tube, means connected to said gating tube for adjusting the bias of said gating tube comprising a second tube having a cathode circuit comprising an impedance in the cathode circuit of said gating tube, and means for adjusting the current flow through said second tube.

HARVEY KARP.V

ROBERT R. DARDEN, J R.

MICHAEL F. KOLODZIEJ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'IEINTSV Number Name Date 2,092,496 Branson Sept. 7, 1937 2,300,999 Williams Nov. 3, 1942 2,338,395 Bartelink Jan. 4, 1944 2,405,231 Newhouse Aug. 6 1946 2,438,717 Puckette Mar. 30, 1948 2,460,061 Chapin Jan. 25, 1949 2,482,544 Jacobsen Sept. 20, 1949 

